1. Field of the Invention
The present invention relates to a sheet binding apparatus for binding a sheet bundle including a plurality of sheets and an image forming apparatus provided with the sheet binding apparatus.
2. Description of the Related Art
There has been widely used a stapling unit for binding a sheet bundle including a plurality of sheets by using a stapling member such as a metallic staple as a sheet binding apparatus for binding together sheets having images formed thereon by an image forming apparatus such as a copying machine or a printer.
However, in the case where each of the sheets in the stapled sheet bundle is used as a original to be read in a copying operation, the staple in the sheet bundle need to be removed. Otherwise, also in the case where the stapled sheet bundle is recycled, the staple in the sheet bundle need to be removed to be recycled separately from the sheet from the viewpoint of environmental issues. In either case, cumbersome work is needed. In addition, the staple is wasted after the use, thereby inducing a profligate use of resources.
In view of the above, there has been proposed an apparatus provided with a sheet binding portion having concave portions and convex portions, which forms concavity and convexity on a part of a sheet bundle conveyed to a stapling position, as a sheet binding apparatus in which cumbersome work in reusing sheets as originals or recycling the sheets is alleviated and the profligate use of resources is reduced without using any staple.
However, in a sheet binding apparatus disclosed in Japanese Patent Application Laid-open No. 2004-155537, concave portions and convex portions which constitute a sheet binding portion are formed into engageable sizes (i.e., into the same shape). Therefore, the concave portions and convex portions are brought into contact with each other in substantially the entire area via a sheet bundle when the concavity and the convex portion are formed on the sheet bundle. As a consequence, as the thickness of the sheet bundle becomes greater, a contact resistance becomes larger at the time of the formation of the concavity and the convex portion on the sheet bundle, thereby requiring a greater pressing force.
The number or arrangement of concavity and convex portion to be formed on the sheet bundle is changed in the sheet binding apparatus disclosed in Japanese Patent Application Laid-open No. 2004-155537 in order to perform a binding operation according to the thickness of the sheet bundle. However, in order to change the number or arrangement of concavity and convexity to be formed on the sheet bundle, it is necessary to replaceably provide a plurality of sheet binding portions in which numbers or arrangements of concavity and the convexity are different or provide a moving mechanism for moving the relative position between the sheet binding portion and the sheet bundle. In other words, a problem of a complicated configuration arises.
In view of the above, an object of the present invention is to provide a sheet binding apparatus capable of forming concavity and the convexity on a sheet bundle by a predetermined pressing force with a simple configuration irrespective of the thickness of the sheet bundle.